1. Field of the Invention
This invention relates generally to exhaust systems. More particularly, the invention relates to an exhaust muffler for a multi-cylinder internal combustion engine.
2. Description of the Related Art
Generally, vehicle manufacturers design exhaust systems to comply with sound attenuation and emission requirements. However, performance engines used in vehicles such as sports cars are often designed to maximize power output. The maximum power output often occurs at higher engine speeds. At these high speeds, exhaust system backpressure can limit the operational envelope of the performance engine. A significant source of the backpressure in the conventional exhaust system is a muffler.
The muffler design further changes the exhaust sound by way of restriction, absorption, or reflection methods alone, or with their combination. As the exhaust gas is passed through the muffler, the sound wave energy associated with the exhaust gas is converted into heat and is dissipated. The muffler accomplishes this task with the use of metal plates, tubes, insulation, and/or chambers with a series of holes or perforations along with one of the three methods mentioned above. Typical OEM designs use restriction type mufflers which force the exhaust gas through a long arduous path, often including a chamber and/or reversing the direction of the gas flow. Restriction muffler designs maximize their sound deadening ability at the significant cost of reducing engine performance and fuel economy.
An example of an absorption method is a muffler design that sends the exhaust gases through a chamber by way of at least one straight through pipe that is perforated and wrapped with insulating material, for example, steel wool or fiberglass. The selection of chamber size and whether the design will incorporate baffles will dictate the advantages and disadvantages presented by the selected design. For example, if a chamber is selected with a diameter slightly greater than the through pipe, the sound attenuation will be minimal; however, minimal back pressure will be introduced into the exhaust system. In designs that use a much larger chamber than the straight through pipe, the sound attenuation will be increased, however, an increase in back pressure will be incurred. With this design, as the exhaust gasses enter the large chamber, they expand and slow down dramatically whereby they dwell longer in the insulating insulation, and thus absorb more noise. The larger chamber gently tapers back into the smaller size of the exhaust pipe. Reflective mufflers utilize absorption principles in conjunction with reflection to minimize noise by colliding out of phase sound waves to cancel each other.